You've got a sticking cutout relay. Has the regulator been adjusted, or was it simplly installed without checking? A lot of the aftermarket regulators being sold now are very poor quality, or at least they're seriously out of adjustment "as received". Once the cutout sticks once and the points are damaged, it will become a chronic problem. If possible, it would be a very good idea to locate an original-equipment Delco-Remy regulator, either new old stock, or at least a good-condition used unit, then have someone who knows what he's doing adjust it correctly. There are three critical adjustments, closing voltage, current regulator, and voltage regulator. The most common cause of a sticky cutout relay is low closing voltage. The cutout should not try to close before the armature voltage reaches 6.5-6.75 volts. Most 6 volt generators need a current regulator adjustment of 25-30 amps, and a voltage regulator adjustment of 7.5 volts against a fully-charged battery.
All of the adjustment numbers will drop slightly as the cover is installed, due to the steel cover being a better conductor of magnetism than air.
If you don't have a good supplier of electrical parts, PM me for a suggestion where to find a good source. The PC patrol zaps my posts too often, even when I try to give stuff away!
OOPS! Just re-read your post and discovered you've converted to 12 volts. Closing voltage should be 12.5-12.75, current regulator 35 amps, and the voltage regulator setting should be 14.0-14.7 volts.
Jerry
